1. Field of the Invention
The present invention relates to a structure of a laser diode. More particularly, the present invention relates to a structure of a high power edge emission laser diode.
2. Description of the Prior Art
During the recent years, the society and economy are highly developed and the technology advances in many aspects of people's daily life, the Laser Diode (LD) is a key component for the optical storage, optical communication and medical laser. Because the market of low power LD applied for the optical storage reader is saturated gradually, the specification of LD goes toward the high power applications such as a rewritable optical storage reader, a communication pump LD with a wavelength of 980 nm, a green light pump LD with a wavelength of 808 nm, a full-color laser projector and a full-color projection television (TV) using the high power LD, which all of the aforementioned high power LDs need to have small size and long lifetime.
Normally, increasing the vertical mode size of the edge emission LD can lower the optical output power density to enhance the output power and narrow the vertical divergence angle. A small vertical divergence angle can reduce the coupling loss between the edge emission LD and the optical components to increase the input optical power of the receiving-end, so as to simplify the design of the optical devices.
A conventional technology is reducing the thickness of the confinement layer of the edge emission LD to lower down the optical power density on the mirror surface of the LD and reduce the divergence angle of the far field, but it will also lower the confinement factor (Γ) to make operation efficiency of the LD mirror surface decline at the same time.
Another conventional technology is to design the LD as asymmetric cladding layers and make the near field pattern incline towards the n-type cladding layer to reduce the optical absorption.
In order to further reduce the far field divergence angle, another conventional technology is to add a design of a mode extension layer. That means to add a high refraction index material near the active layer to make the light distribution confined near the active layer extend to the high refraction index layer. However, this method will significantly lower the confinement factor and easily deteriorate the far field pattern at the same time, and will furthermore cause a multi-mode oscillation and a kink phenomenon owing to the mutual switching.